In different fields of application, battery-powered handpieces and their charging stations are necessarily in contact with liquids, and there is a need to protect electrical contacts of such battery-powered handpieces and their charging stations from liquids, or to keep the contacts dry. User manuals or labels of such battery-powered devices give instructions to the user as to avoid liquids and to keep the contacts dry. However, it can be experienced that in current practice, these instructions are not considered or followed in every case. Furthermore, fluid films on the contacts may be present even if these instructions are complied with because fluid films are not necessarily visually observable. For example by wiping the battery-powered device and its charger device with a moist cloth, the remaining liquid film may still be sufficient to cause some weak corrosion, even if the fluid or agent vaporises after a few minutes. If a longer period of time is considered, the incremental corrosion of the contacts will affect the electrical properties of the contacts.
Unlike contacts at commonly used plugs, it is not useful to protect charging contacts of battery-powered electrical devices by sealing covers or means that would protect them from liquids that may be used in combination with such devices. It is rather useful and desirable that such charging contacts are open and easily accessible because placing the battery-powered device into the charging station and the charging operation should be easy and quick. Such contacts are typically realised by metallic elements on one component, e.g., the handpiece, and are placed somewhere at the surface of the housing. The other component, e.g., the charging station, may have metallic pins or stripes or the like sticking out of the housing of the charging station in order to allow a proper electrical contact whenever the handpiece is placed into the charger station. Thus, fluids used with the device may flow to the charging contacts, and in particular in the region of the housing separating the contacts. Furthermore, if these fluids are electrically conductive, an electric current may flow between the contacts. This currents initiate an electro-chemical reaction which in turn leads to a corrosion of the contacts. Corroded contacts, in turn, result in increased contact resistances. Significant electrical power will drop at the contacts and heat them up. The increased resistance will affect a proper charging procedure, and will in the end totally hinder the re-charging of the battery.
The presence of such fluids is quite common, especially with electro-medical devices, such as dental curing lights, since such devices are treated with cleaning or disinfectant agents quite frequently.